JP3089332B2 - Lightwave rangefinder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electro-optical distance meter provided with a conversion means for converting an input pulse signal into an attenuated oscillation waveform, and more particularly, to a plurality of light source units tuned to a tuned amplifier circuit. The present invention relates to a lightwave distance meter that emits a pulse and generates a damped oscillation waveform having a large output amplitude by a tuned amplifier circuit, so that a measurement limit distance is long and high-precision measurement can be performed.

[0002]

2. Description of the Related Art In a conventional pulse-type lightwave distance meter, an external distance measuring optical path and an internal reference optical path are switched by an optical chopper. When the optical chopper selects the external distance measuring optical path, the light emitting pulse emitted from the light emitting source is reflected by the corner cube of the object to be measured, and received by the light receiving element in the light wave distance meter as a light receiving pulse. That is, the light emission pulse shown in FIG. 7A is reflected by the corner cube,
The light is received as the light receiving pulse shown in FIG. The conventional lightwave distance meter converts the electric signal converted by the light receiving element into a damped oscillation waveform shown in FIG. 7C by a tuning amplifier, and detects a cross point X with respect to 0 V using a comparator. 7 (d) is obtained. The measurement distance in the external ranging optical path is
The time T ₂ from the light emission of the light emitting diode to the light receiving timing signal shown in FIG.
The measurement was performed by using the rough measurement using the reference clock and the precision measurement by the precision interpolation means shown in FIG.

When an internal reference light path is selected by an optical chopper, a light emission pulse emitted from a light source passes through the internal reference light path and is received by a light receiving element as a light reception pulse shown in FIG. Then, the electric signal converted by the light receiving element is converted into a damped oscillation waveform shown in FIG. 7F by a tuning amplifier, and a light receiving timing signal shown in FIG. 7G can be obtained. From the light emission of the light emitting diode, FIG.
The time T ₁ until the light receiving timing signal shown in FIG. The distance in the internal reference light path was also obtained by performing the same processing as the external reference light path, and the distance from the optical distance meter to the corner cube was obtained by subtracting the distance in the internal distance measurement light path from the external distance measurement light path. .

There is a fluctuation of air between the lightwave distance meter and the corner cube, and the pulse received by the lightwave distance meter varies from a1 to a2 as shown in FIG. Accordingly, the damped oscillation waveform from the tuning amplifier
As shown in FIG. 8 (b), it changes from b1 to b2. However, the cross point X between the damped oscillation waveform and 0V
Is constant regardless of the peak value of the damped oscillation waveform. Therefore, the method of converting the received pulse into a damped oscillation waveform by the tuning amplifier is not affected by the fluctuation of the received pulse. Therefore, as shown in FIG. 8C, if the comparator output C having the cross point X as the reception time is used as the reception timing signal, it is possible to provide a lightwave distance meter which is not affected by the fluctuation of the received light pulse.

[0005]

However, since the above-described pulse type light wave distance meter measures the coarse measurement distance and the precision measurement distance simultaneously, the pulse light is reflected from the corner cube which is the object to be measured, and the light wave distance meter is used. Until it returns to the main body, there is a problem that the next pulse cannot be emitted. That is, as shown in FIG. 9 (a), the light emitting pulses P1, P2 When emits light repeatedly like a ..., pulse electronic distance of reflected to the distance L ₁ from the placed corner cube FIG. 9 (b)
FP1 shown in FIG. While the distance L ₁ by using a coarse measurement distance and fine measurement distance when this can be uniquely determined, if the further corner cube was in a position distant L ₂ are received pulse light wave rangefinder 9C, there is a problem that it cannot be determined whether the light receiving pulse FP2 is the reflected light of the light emitting pulse P1 or the reflected light of the light emitting pulse P2.

That is, when the light receiving pulse is FP2, it cannot be determined whether the distance to the corner cube is L ₂ or L ₂ dash. For this reason, the pulse-type lightwave distance meter has a limitation that the interval between the emission pulses must be longer than the measurable limit distance of the lightwave distance meter than the time interval between reciprocation of the pulsed light.

Since the measurable distance of a normal pulse type light wave distance meter is about 20 km, the repetition frequency fp of the light emission pulse is

Fp = 2 * (20 km / C) (H
z) where C = speed of light = 7.5 KHz

## EQU1 ## Therefore, the repetition frequency of the light emission pulse of a general pulse type lightwave distance meter is selected from several hundred Hz to about 5 KHz.

In order to avoid the limitation of the repetition frequency of the emission pulse, a method of separately measuring the emission interval of the emission pulse between the observation of the coarse measurement distance and the observation of the precision measurement distance may be considered. In addition, there is a problem that measurement time is required, and when the corner cube is moving, an error occurs when combining the coarse measurement distance observation value and the precision measurement distance observation value, which is not practical.

Further, from the viewpoint of improving the precision of the precision measurement value, it is desirable that the pulse width of the emission pulse is narrow. However, the pulse laser diode used as a light source can be used only with a very small light emission duty. Generally, the light emission pulse width is about 10 nSEC due to the limitation of the frequency characteristics of the tuning amplifier. Assuming that the repetition frequency of the light emission pulse is 5 KHz, the light emission duty Dp is

Dp = 10 nSEC / (1/5 KHz) = 0.005%

## EQU1 ##

Although it is possible to use a narrower pulse to increase the measurement accuracy, the light emission duty is further reduced. However, the maximum rating of the light emission duty of the pulse laser diode is about 0.1%.

Under the condition of a small light emission duty, the peak power of the light emission pulse light may be able to be used exceeding the absolute maximum rating in some cases.

“Emission peak power” * “Pulse width” = constant

Most of the pulse laser diodes do not satisfy the above relationship, and the improvement of the emission peak power could not be expected so much.

That is, in the conventional pulse-type lightwave distance meter, it is difficult to improve the accuracy by increasing the light emission frequency of the light emission pulse and increasing the averaging effect by repetition, and the width of the light emission pulse must be narrowed. There is a problem that the light emission characteristics of the pulse laser diode used as the light source cannot be used effectively due to the restriction that the light source cannot be used.

[0019]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has a light source unit that emits light in a pulsed manner and an optical unit for transmitting light from the light source unit to an object to be measured. Means, light receiving means for receiving reflected light from the object to be measured, and converting the light into a received pulse of an electric signal, and tuning amplifying means for converting the received pulse converted by the light receiving means into an attenuated oscillation waveform And a reception timing detection unit for forming a reception timing signal from the damped oscillation waveform converted by the tuning amplification unit, and a distance between the object to be measured and a time difference from light emission of the light source unit to the reception timing signal. The light source unit is configured to emit a plurality of pulses tuned by the tuning amplifier circuit.

The present invention also provides a light source unit that emits light in a pulsed manner, optical means for transmitting light from the light source unit to an object to be measured, and light reflected from the object to be measured. Light receiving means for converting the received pulse converted by the light receiving means into a damped oscillation waveform, and a threshold for the damped oscillation waveform converted by the tuning amplification means. Reception timing detection means for detecting a cross point with respect to a level and forming a reception timing signal, and distance measurement means for measuring a distance from a light emission from the light source unit to a measurement target from a time difference of the reception timing signal. Wherein the reception timing detecting means comprises:
Among the plurality of cross points detected from the damped oscillation waveform, at least two or more cross points are configured to be a reception timing signal, and the light source unit outputs a plurality of pulses tuned by the tuning amplifier circuit. It is configured to emit light.

[0021] The present invention, when the light source unit for pulsed light emission is, the time that the light source emits light is T, a time when the light source does not emit light existing between the light emission and light emission of the light source was T _2,

T ₂ = (2n + 1) T (n is an integer)

It is also possible to configure the following relationship.

Further, the present invention can be configured such that the time during which the light source emits light and the time during which the light source existing between the light emissions does not emit light are the same time T.

[0025]

According to the present invention configured as described above, the light source unit emits a plurality of pulses tuned to the tuning amplifier circuit, and the optical unit transmits light from the light source unit to the object to be measured. The light receiving means receives the reflected light from the object to be measured and converts the reflected light into a received pulse of an electric signal. The tuning amplifying means converts the received pulse converted by the light receiving means into an attenuated oscillation waveform, and the receiving timing detecting means forms a receiving timing signal. Further, the distance measuring means measures the distance to the object to be measured based on the time difference from the light emission of the light source unit to the reception timing signal.

Further, according to the present invention, the reception timing detecting means detects a cross point with respect to a threshold level of the damped oscillation waveform converted by the tuning amplifying means, and detects at least two or more cross points among the plurality of detected cross points. The point is used as a reception timing signal.

According to the present invention, the light emission time of the light source is defined as T.
And T ₂ is the time during which the light source existing between the light sources does not emit light,

T ₂ = (2n + 1) T (n is an integer)

In this connection, the light source unit may emit light in a pulsed manner.

The light source section can emit light in a pulsed manner in a relation of T = T ₂ .

[0031]

【Example】

An embodiment of the present invention will be described with reference to the drawings.

As shown in FIG. 1, the lightwave distance meter of this embodiment comprises a laser diode 1, a condenser lens 2, a condenser lens 3, and a pair of split prisms 41, 42.
, Optical path switching chopper 5, internal optical path 6, APD
71, an optical fiber 8, a prism 9, and an objective lens 10. And corner cube 11
Corresponds to an object to be measured arranged at a position distant from the main unit of the electro-optical distance meter, and has a function of reflecting an optical pulse.

Laser diode 1 and condenser lens 2
1, 22, light emitting side optical fiber 81, and split prism 41
, The prism 9 and the objective lens 10 correspond to optical means.

The laser diode 1 corresponds to a light source unit. The laser diode 1 of this embodiment employs a pulse laser diode, has a relatively large peak power, and has a duty ratio of about 0.01%. Waves can be generated. The optical path switching chopper 5 switches light beams. The light receiving element 7 corresponds to light receiving means, and any element that can receive the pulse light emitted from the laser diode 1 is sufficient.

The split prism 41 is composed of a first half mirror 411 and a second half mirror 412, and the split prism 42 is composed of a first half mirror 421 and a second half mirror 422. I have. The optical fiber 8 includes a light emitting side optical fiber 81 and a light receiving side optical fiber 82.

When the light emission pulse train is emitted from the laser diode 1, the light emission pulse train is coupled to the input end 81 a of the light emitting side optical fiber 81 by the condenser lenses 21 and 22. The light emission pulse train emitted from the output end 81 b of the light emission side optical fiber 81 is sent to the split prism 41. The pulse train transmitted through the first half mirror 411 of the split prism 41 can be emitted to the external distance measuring optical path via the optical path switching chopper 5. The light is reflected by the first half mirror 411 of the splitting prism 41 and further reflected by the second half mirror 4.
The pulse train reflected by 12 is transmitted to the optical path switching chopper 5
The light can be emitted to the internal distance measuring optical path 6 via. The optical path switching chopper 5 is for switching between the internal ranging optical path 6 and the external ranging optical path. Therefore, when the optical path switching chopper 5 selects the external distance measuring optical path, the pulse train is reflected by the prism 9 and then emitted to the outside by the objective lens 10.

The pulse train emitted from the objective lens 10 is reflected by the corner cube 11, and is again returned to the objective lens 1.
The light is received at 0 and sent to the prism 9. The received pulse train is reflected by the prism 9 and sent to the splitting prism 42, and the received pulse light transmitted through the first half mirror 421 of the splitting prism 42 is coupled to the light receiving end 82 a of the light receiving side optical fiber 82.

When the optical path switching chopper 5 selects the internal distance measuring optical path 6, the light emission pulse train is sent to the split prism 42 through the internal distance measuring optical path 6. The light pulse train is reflected by the first half mirror 421 and the second half mirror 422 built in the split prism 42,
The light receiving end 82a of the light receiving side optical fiber 82 is coupled to the light receiving end 82a.

The emitting end 8 of the light receiving side optical fiber 82
The light pulse train emitted from 2b is
It is designed to bind to APD71 by 1, 32,
The light is converted into a current pulse by the light receiving element 7.

Next, the configuration of the electric circuit of this embodiment will be described in detail.

(First Embodiment)

A first embodiment shown in FIG.
0, the first frequency divider 110, the synthesizer 120, and the second
Frequency divider 130, timing circuit 140, laser diode 1, laser diode driver 150, and APD 7
1, tuning amplifier 160 and reception timing detection circuit 170
, A counter 180, a peak hold circuit 190, a level determination circuit 200, a band pass filter 210, a sample / hold (S / H) 220, a switch 230, an AD converter 300, a memory 400, and a CPU 500.

The crystal oscillator 100 is one of the reference signal generating means, and generates a 15 MHz reference signal.
This reference signal is supplied to a first frequency divider 110, a synthesizer 130, a bandpass filter 210, and a counter 180. The reference signal supplied to the first frequency divider 110 is divided into 1/100 by the first frequency divider 110 to become 150 KHz and is sent to the synthesizer 130. The synthesizer 130 generates 15.15 MHz from the 150 KHz supplied from the first frequency divider 110 and the 15 MHz supplied from the crystal oscillator 100, and sends out 15.15 MHz to the second frequency divider 130. Second frequency divider 13
0 is 15.15 supplied from synthesizer 130
The frequency is divided into 1/50 to produce 303 KHz, which is sent to the timing circuit 140. Note that the first frequency divider 110, the second frequency divider 130, the synthesizer 12
The output signal of 0 is a binarized signal.

The timing circuit 140 sends a pulsed laser emission timing signal to the laser diode driver 150, and the timing circuit 140 sends a reset signal to the peak hold circuit 190 having a damped oscillation waveform. I have. Note that the capacitor charge signal, the pulse laser emission timing signal, and the reset signal for the peak hold circuit 190 are all 3
This signal is repeated at 030 Hz.

Then, the laser diode driver 150
Drives the laser diode 1 in a pulsed manner in accordance with a pulsed laser emission timing signal of the timing circuit 140.

Here, the laser diode driver 150
Will be described in detail. Here, the capacitor charge signal is set to CS, the reset signal for the peak hold circuit 190 is set to RS, and the pulse laser emission timing signal P
S.

First, the operation of the laser diode driver 150 for the reset signal RS, the capacitor charge signal CS, and the pulsed laser emission timing signal PS for the peak hold circuit 190 will be described with reference to FIG.

The laser diode driver 150 includes a first transistor 1501 and a second transistor 15.
02, the third transistor 1503, and the coil 150
4, a first diode 1505, a second diode 1506, a first capacitor 1507, a second capacitor 1508, and a delay circuit 1510. A signal is input to the laser diode driver 150 in the order of the capacitor charge signal CS and the pulse laser emission timing signal PS.

The capacitor charge signal CS is H
turning on the first transistor 1501 during igh;
It has become like passing a current I _L to the coil 1504. When the capacitor charge signal CS becomes LOW, the coil 15
The energy stored in 04 is stored as electric charge in the first capacitor 1507 via the first diode 1505 for rectification, and similarly stored as electric charge in the second capacitor 1508 via the second diode 1506. .
After that, the pulse laser emission timing signal PS is sent to the second transistor 1502 and the delay circuit 1510. The second transistor 1502 and the third transistor 1503 are avalanche transistors. Second
The transistor 1502 receives the pulsed laser emission timing signal PS and causes the charge stored in the second capacitor 1508 to flow through the laser diode 1 to emit pulsed light. On the other hand, the delay circuit 1510
Delays the pulse laser emission timing signal PS for a certain period of time, and sends the delayed pulse laser emission timing signal PS to the third transistor 1503. The third transistor 1503 causes the charge stored in the first capacitor 1507 to flow through the laser diode 1 to emit pulsed light in response to the input of the delayed pulsed laser emission timing signal PS.

As shown in FIG. 3B, the delay circuit 1510 starts the second light emission pulse by the third transistor 1503 after the end of the first light emission pulse by the second transistor 1502.
The emission of light emission pulses, which delays by a time T _2, in this embodiment,

T ₁ = T ₂ = T ₃

The setting is made as follows. The light emission train by the two pulse lights repeats at 3030 Hz.

The light pulse emitted from the laser diode 1 passes through the optical system and is received by the APD 71. The APD 71 is one of the light receiving elements 7, and is a diode that can apply a deep bias to a pn junction to induce a nasal multiplication and obtain a gain. The APD 71 receives an optical pulse that has passed through the internal reference optical path and an optical pulse that has passed through the external ranging optical path. The light pulse is converted into an electric signal of a current pulse train by the APD 71 and sent to the tuning amplifier 160.

The tuning amplifier 160 converts the current pulse train input from the APD 71 into a voltage signal, converts it into a damped oscillation waveform, and performs inversion amplification. The damped oscillation waveform formed by the tuning amplifier 160 is supplied to a reception timing detection circuit 170 and a peak poled circuit 190.

The tuning amplifier 160 has a center frequency f ₀
But

F ₀ = 1 / (T ₁ + T ₂ )

By setting the Q of the tuning circuit to an appropriate value (for example, about Q = 5), a damped oscillation waveform as shown in FIG. It is for output.

Further, the pulse width as shown in FIG.
Have equal spacing

T ₁ = T ₂ = T ₃

With respect to the pulse train of FIG. 4, the output of the tuning amplifier 160 includes a damped oscillation waveform (FIG. 4E) by the first pulse d1 and a damped oscillation waveform by the second pulse d2 of the pulse train shown in FIG. FIG. 4 which is the sum with (FIG. 4 (f))
The waveform shown in (g) is obtained, and there is an excellent effect that a damped oscillation waveform several times that of FIG. 4A can be obtained.

As shown in FIG. 1, the reception timing detection circuit 170 comprises a first comparator 171, a second comparator 172, a one-shot vibrator 173, a rising edge detector 174, and a falling edge detector 175. I have. The first comparator 171 has a threshold level V _S1 , captures the g1 portion of the damped oscillation waveform in FIG. 4 (g), confirms light reception, and activates the second comparator 172 having a threshold level 0V for a predetermined time. The active state is set. Then, the second comparator 172 captures two points g3 and g4, which are cross points with 0V of the damped oscillation waveform, and receives a reception timing signal having a width corresponding to the part of g2 (FIG. 4 (h)).
Is output.

In the case of the damped oscillation waveform shown in FIG. 4G, since the amplitude of g2 to g5 is maximum, the slope of g4 is the steepest, and is hardly affected by error factors. Therefore, the falling part of the waveform in FIG. 4H is used as the reception timing signal. For the waveform after g5, the active state of the second comparator 172 has been terminated, and the comparator does not operate.

A rising edge detector 174 and a falling edge detector 175 are connected to the output side of the second comparator 172, and the output signal of the rising edge detector 174 is output to the first sample and hold circuit 2.
The output signal of the falling edge detector 175 is sent to the second sample and hold circuit 222. The cross point between the damped oscillation waveform and 0 V may be detected at two or more points.

The reception timing detection circuit 170 supplies a reception timing signal to the sample / hold (S / H) 220 and the counter 180. Counter 18
“0” is reset by a reset signal from the timing circuit 140, and the time until the reception timing signal is counted by 15 MHz from the crystal oscillator 100. That is, the rising edge detector 174
Is supplied to the counter 180, and the counter 180 is connected to the rising edge detector 17.
Until the signal from 4 is input, 15 MHz from the crystal oscillator 100 is counted.

The 15 MHz transmitted from the crystal oscillator 100 to the band-pass filter 210 becomes a sine wave and is transmitted to the first sample-hold circuit 221 and the second sample-hold circuit 222. Then, the first sample and hold circuit 221 performs sample and hold based on the output signal of the rising edge detector 174, and the second sample and hold circuit 222 performs sample and hold based on the output signal of the falling edge detector 175. I have. The waveform signal sampled and held by the sample and hold circuit 221 and the second sample and hold circuit 222 is
0, and the switching unit 230 is switched according to a switching signal from the CPU 500. The waveform signal switched by the switch 230 is AD-converted by the AD converter 300, and the converted digital data is stored in a predetermined memory 400. When the AD conversion ends, a conversion end signal is output to the CPU 500.

The damped oscillation waveform sent from the tuning amplifier 160 to the peak hold circuit 190 is peak-held by the peak hold circuit 190 and becomes a DC level signal corresponding to the peak value of the damped oscillation waveform.
Sent to 0. The level determination circuit 200 receives the signal from the peak hold circuit 190, and determines that the light amount of the light receiving pulse train is A
It is determined whether or not the PD 71, the tuning amplifier 160, and the reception timing detection circuit 170 are in a proper operating range, and the result is sent to the CPU 500. CPU4
The counter 31 receives the signal from the level determination circuit 200 and only receives the signal from the light receiving pulse train when the light amount is an appropriate value.
The counter value from 0 and the data from the AD converter 300 are adopted.

Further, the peak hold circuit 190 is reset every time a light emission pulse train is emitted by a reset signal from the timing circuit 140, so that the amount of light can be determined each time an emission pulse is emitted. Therefore, it is possible to minimize the adverse effect due to the fluctuation of the received light amount due to the fluctuation of the air between the main body of the lightwave distance device and the object to be measured.

15 MH sent from crystal oscillator 100
The sine wave obtained by passing z through the band-pass filter 210 and the light emission frequency of 3030 Hz of the laser diode 1 are slightly shifted. For this reason, as shown in FIG. 5A, the phase relationship between the reception timing signal and the sine wave obtained through the band-pass filter 210 also slightly shifts. This phase shift amount is

(1/3030 Hz) / (1/15 MHz) = 4950 + (50/101)

And becomes “50/101”.

Each light emission pulse train and the bandpass filter 2
As shown in FIG. 5B, the phase relationship with the sinusoidal sine wave signal obtained through 10 is such that 101 cycles constitute one cycle, and the 102nd emission pulse train is 1 cycle.
It has the same phase relationship as the first time. For this reason,
The output signal of the sample hold (S / H) 220 is

F = 3030 Hz / 101 = 30 Hz

Although the period becomes one cycle and does not become a sine wave as shown in FIG. 5C, the rearrangement is performed at the stage of storing the data in the memory 400 after the AD conversion, so that the waveform is changed as shown in FIG. The horizontal axis is the address on the memory 400, and the vertical axis is AD
When converted value data is used, AD conversion data having a sine wave shape can be created. Further, the sample-and-hold data and the A / D-converted data by the light emission pulse train after the 102nd time are the data after the second cycle of 30 Hz. Therefore, if the judgment result of the level judgment circuit 200 is appropriate, the data of the previous cycle is obtained. And then averaging the data to improve the accuracy of the A / D converted data.

The first sample and hold circuit 221
Using the AD conversion data obtained by the above and the AD conversion data obtained by the second sample-and-hold circuit 222, a phase is obtained by performing a Fourier transform on each data, and an operation of averaging this value is performed. It is configured to use this average value.

The laser diode 1 executed as described above
From the emission of light to the storage of the AD-converted data in the memory 400 are performed for the external distance measuring optical path and the internal reference optical path. As shown in FIG. 5D, if is assumed to be AD conversion data of the internal reference optical path and is assumed to be AD conversion data of the external distance measuring optical path, the phase difference φ between the two waveforms corresponds to the optical path difference. Fourier transform is performed on each waveform to obtain phase information of the fundamental component wave, and a precise measurement distance of 10 m or less can be obtained from the phase difference. The coarse measurement distance can also be determined with an accuracy of 10 m from the counter difference of the counter 180 between the external distance measuring optical path and the internal reference optical path. Then, by combining the coarse measurement distance and the precision measurement distance, the actual distance from the optical distance meter to the object to be measured can be obtained. A configuration for performing these operations corresponds to a distance measuring unit.

Note that the precise measurement distance is obtained by performing a Fourier transform on the AD-converted data value to obtain the phase of the fundamental wave component. Therefore, the waveform to be sampled and held is not necessarily a sine wave shown in FIG. Need not be
The integrated wave shown in FIG. 6B or the triangular wave shown in FIG. Similarly, a low-pass filter can be employed instead of the band-pass filter 210.

In the first embodiment configured as described above, the AD sample obtained by the first sample and hold circuit 221 is used.
The conversion data and the AD conversion data obtained by the second sample-and-hold circuit 222 are used to perform a Fourier transform on each of the data to determine the phase and average the values. There is an excellent effect that the offset of the second comparator 172 of the timing detection circuit 170 can be removed.

(Second Embodiment)

Next, a second embodiment will be described with reference to FIG. In the first embodiment, the first sample and hold circuit 2
21 and a second sample-and-hold circuit 222. The first sample-and-hold circuit 221 performs sample-and-hold by an output signal of the rising edge detector 174, and the second sample-and-hold circuit A sample and hold 222 is performed by the output signal of the falling edge detector 175.
The signal after the sample hold is switched by the switch 230.

In the second embodiment, the sample and hold circuit 22
Using only one 0, the output signal of the rising edge detector 174 and the output signal of the falling edge detector 175 are switched by the switch 230, and the switched output signal is sent to the sample and hold circuit 220. Have been.

The second embodiment has a disadvantage that the same damped oscillation waveform cannot be measured when measuring the rising edge and the falling edge. However, the first embodiment can be performed if the measurement is performed alternately in a short time. There is an effect that the same operation as can be performed. The other configuration and operation are the same as those of the first embodiment, and thus the description is omitted.

In the above embodiment, the number of light pulses constituting the light emission pulse train is two. However, the light pulse train may be constituted by three or more light pulse trains. In this case, the output amplitude of the damped oscillation waveform is further increased. This has the effect of increasing the size. It is desirable that the reception timing detection circuit 170 be configured to capture the maximum slope portion of the damped oscillation waveform.

Further, in the above embodiment, only the portion g4 of the damped oscillation waveform in FIG. 4G is used as the reception timing. However, a cross point with another 0V, such as g3 and g6, is used as the reception timing. May be used. Then, by performing an averaging operation with the data obtained by g4, the second comparator 17 of the reception timing detection circuit 170 is obtained.
In addition, the drift of the threshold level of 2 can be removed, and the measurement accuracy can be improved by the averaging effect.

[0085]

According to the present invention having the above-described configuration, a light source unit that emits light in a pulsed manner, an optical unit for transmitting light from the light source unit to an object to be measured, and a light source from the object to be measured. A light receiving means for receiving the reflected light and converting it into a received pulse of an electric signal, a tuned amplifying means for converting the received pulse converted by the light receiving means into an attenuated oscillation waveform, Reception timing detection means for forming a reception timing signal from the damped oscillation waveform,
A light-wave distance meter comprising a distance measuring means for measuring a distance to the object to be measured, based on a time difference from the light emission of the light source unit to the reception timing signal; Because it is configured to emit a plurality of pulses tuned by the amplifier circuit, it is possible to obtain a damped oscillation waveform whose output amplitude is several times larger than that of the conventional lightwave distance meter, and the measurement distance limit And the measurement accuracy can be increased.

Further, since a plurality of pulses are emitted, there is an effect that the emission characteristics can be utilized to the maximum without exceeding the maximum rating of the pulse laser or the like used as the emission source.

[0087]

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a first exemplary embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a second exemplary embodiment of the present invention.

FIG. 3 is a diagram illustrating a configuration of a laser diode driver according to the present embodiment.

FIG. 4 is a diagram illustrating detection of a reception timing signal according to the embodiment;

FIG. 5 is a diagram illustrating phase difference measurement according to the present embodiment.

FIG. 6 is a diagram illustrating waveforms sampled and held in the present embodiment.

FIG. 7 is a diagram illustrating the principle of a conventional lightwave distance meter.

FIG. 8 is a diagram illustrating a light receiving pulse of a conventional lightwave distance meter.

FIG. 9 is a diagram illustrating a light receiving pulse of a conventional lightwave distance meter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser diode 2 Condenser lens 3 Condenser lens 41 Split prism 42 Split prism 5 Optical path switching chopper 71 APD 8 Optical fiber 9 Prism 10 Objective lens 11 Corner cube 160 Tuning amplifier 170 Reception timing detection circuit 171 First comparator 172 Second comparator 173 One-shot vibrator 174 Rising edge detector 175 Falling edge detector 180 Counter 190 Peak hold circuit 220 Sample hold circuit 230 Switching device 300 AD converter 400 Memory 500 CPU 1000 Operation processing means

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01S ⁷ /48-7/64 G01S 17/00-17/95 G01S 15/00-15/96

Claims (4)

(57) [Claims] A light source unit that emits light in a pulsed manner, optical means for transmitting light from the light source unit to an object to be measured, light reflected from the object to be measured, and an electric signal A light receiving means for converting the received pulse converted by the light receiving means into a damped oscillation waveform; a reception timing signal from the damped oscillation waveform converted by the tuning amplification means; A light-wave distance meter comprising: a reception timing detecting unit for forming a distance; and a distance measuring unit for measuring a distance to an object to be measured by a time difference from light emission of the light source unit to the reception timing signal. A lightwave distance meter, wherein the unit is configured to emit a plurality of pulses tuned by the tuning amplifier circuit. 2. A light source unit that emits light in a pulsed manner, optical means for transmitting light from the light source unit to a measurement target, and light reflected from the measurement target to be received to generate an electric signal. A light receiving means for converting the received pulse converted by the light receiving means into a tuned amplifying waveform; and a crossing for a threshold level of the attenuated vibration waveform converted by the tuned amplifying means. It comprises a reception timing detection means for detecting a point and forming a reception timing signal, and a distance measurement means for measuring a distance from the light emission from the light source unit to a measurement target from a time difference of the reception timing signal. In the optical distance meter, the reception timing detecting means may detect at least two or more cross points among a plurality of cross points detected from the damped oscillation waveform. A lightwave distance meter, wherein the light source unit emits a plurality of pulses tuned by the tuned amplifier circuit, wherein the lightpoint unit is configured to use a point as a reception timing signal. 3. A light source unit for pulsed light emission is, when the light source is a time for light emission is T, a time when the light source does not emit light existing between the light emission and light emission of the light source was _{T 2, T 2 = (2n} + 1 3. The lightwave distance meter according to claim 1, wherein T) (where n is an integer). 4. A time T in which the light source emits light and a time in which the light source existing between the light emission of the light source does not emit light are the same time T.
The lightwave distance meter according to claim 1, wherein: